This invention relates to water soluble polymers prepared by water-in-oil or inverse emulsion polymerization.
Many synthetic and naturally occuring water soluble polymers have been developed which exhibit useful thickening and flocculating properties. These polymers are used in a variety of applications including coatings, textile printing, waste water treatment, oil drilling mud stabilizers, paints and the like. To be most effective, these polymers must be of very high molecular weight.
Although these polymers are commonly available as powders, they are often utilized as aqueous solutions which require the polymers to be hydrated. This is a time consuming step and will often cause the dispersion of solids in the aqueous media to form a gel, which is difficult to handle. In addition, water solutions containing more than 3% by weight of these polymers exhibit too high a viscosity to handle easily.
A significant advance toward overcoming the difficulties associated with the handling of high molecular weight water soluble polymers was the development of the water-in-oil emulsion described in U.S. Pat. Nos. 3,284,393 and 3,826,771. This process utilizes the technique of preparing a fine dispersion of a water solution of soluble monomers into a nonpolar organic phase and subsequently polymerizing the monomers. This allows the preparation of liquid emulsions of a useful low viscosity containing a large proportion of high molecular weight polymer. As the polymer particles are already hydrated, the polymer disperses quickly into water solution upon inverting the water-in-oil emulsion, thereby eliminating the major problem of gel formation during hydration of dry polymers. The inversion of the water-in-oil emulsion is promoted by the addition of surfactants or solid particles as described in U.S. Pat. No. 3,624,019. These emulsions can be prepared utilizing a variety of water soluble monomers and are described in detail in U.S. Pat. Nos. 4,418,237; 3,259,570; and 3,171,805. All of the above listed patents are incorporated herein by reference.
The molecular weight of the polymers formed in these emulsions may vary over a wide range, i.e., 10,000 to 25,000,000. Preferred polymers have molecular weights greater than 1,000,000.
The organic or nonpolar phase is comprised of inert hydrophobic liquids and makes up between 5 and 50% by weight of the emulsion. Commonly used solvents include kerosene, mineral spirits, mineral oils, xylene, or blends of aliphatic and aromatic hydrocarbons. In some cases halogenated solvents have been used to advantage. Preferred solvents would include Isopar M (Exxon Chemicals), which is an example of a branched chain isoparafinic solvent with low aromatic content.
Many water-in-oil emulsifying agents are known in the art and are described in the Atlas HLB surfactant selector. Effective emulsifying agents will have a HLB of less than 15 and preferably less than 10. Most preferably between 4 and 10. These surfactants are added in amounts ranging between 0.1 and 15% by weight of the emulsion and serve to stabilize the dispersion of the monomer/water solution in the hydrophobic phase.
The resulting emulsion is deoxygenated and polymerization is accomplished with a variety of initiator systems. Typical initiator systems include redox systems such as potassium bromate/t-butyl hydroperoxide; ammonium persulfate/sodium metabisulfite; or thermal systems such as azobisisovaleronitrile.
The thickeners and flocculents formed using this process typically have lower than desirable water viscosities upon dissolution. They also have low stability in the presence of an electrolyte, which results in poor rheological properties.